1. Field of the Invention
Exemplary aspects of the present invention generally relate to a process cartridge and an image forming apparatus such as a copier, a printer, a facsimile and the like including the same, and more particularly, to a process cartridge using a rotary brush and a brush housing, and an image forming apparatus including the same.
2. Description of the Background Art
Conventionally, a cleaning brush is provided to a cleaning unit to clean residual toner remaining on a drum-type photoreceptor serving as an image bearing member after a toner image is transferred from the image bearing member. The cleaning brush is generally a rotary brush that contacts the surface of the photoreceptor.
Such a cleaning unit including the rotary brush removes the transfer residual toner either directly with the rotary brush or by dispersing the transfer residual toner with the rotary brush to enable the transfer residual toner to easily pass a contact portion of the photoreceptor, after which the transfer residual toner is removed by a different cleaning member.
In the cleaning unit including the rotary brush, rotation of the rotary brush causes the toner to separate from the photoreceptor surface and the rotary brush, and travel in the air. Consequently, when the toner is dispersed outside the cleaning unit, the toner may stick to a charging member, a transfer member, a developing member, and so forth, thereby contaminating the interior of the image forming apparatus and thus causing charging failure, mottled images, background contamination, and so forth, resulting in deterioration of image quality.
Japanese Patent Unexamined Application Publications No. 2005-17463 and 2005-234481 disclose a cleaning unit in which the rotary brush collects the transfer residual toner by contacting the surface of the photoreceptor.
In an attempt to prevent the toner from being dispersed, the cleaning unit disclosed in Japanese Patent Unexamined Application Publications No. 2005-17463 and 2005-234481 is provided with a housing which covers the rotary brush such that an opening in the housing is located at a position where the rotary brush contacts the photoreceptor.
However, an installation position of the rotary brush and the housing of the cleaning unit according to the related art cleaning units may not adequately prevent the toner from being dispersed externally, for the following reason.
When the rotary brush contacts the photoreceptor while rotating, the toner is dispersed from a downstream end of a place, a so-called “nip”, at which the rotary brush contacts the photoreceptor in the rotation direction of the rotary brush because the tip of the brush is flexed to face upstream of the rotation direction of the rotary brush at the nip.
At the downstream end of the nip in the rotation direction of the rotary brush, when the flexed brush tip separates from the photoreceptor, the flexed brush tip recovers from its flexed state to the original state, and the recovering force of the brush tip brushes and disperses toner on the photoreceptor. Consequently, the toner is dispersed from the downstream end of the nip in the rotation direction of the brush.
The present inventors have observed that, when no gravity acts, the toner getting dispersed from the downstream end of the nip is most likely to travel toward the rotary brush further than a tangent Lt to the surface of the photoreceptor, which is the downstream end of the nip.
In other words, the toner traveling to an orbit farthest away from the rotary brush among other toner getting dispersed from the downstream end of the nip in the rotation direction of the brush is the toner that travels to the direction of the tangent Lt to the photoreceptor surface which is the downstream end of the nip when the toner starts to get dispersed.
The present inventors investigated the relative positions of the rotary brush and the brush housing relative to the photoreceptor, and the toner dispersion.
Referring to FIGS. 8A and 8B, there are provided conceptual diagrams illustrating the photoreceptor and the rotary brush when a downstream nip end E of a nip N in a rotary direction of the rotary brush is positioned substantially higher than the center of rotation 1P of the photoreceptor 1. The nip N is a place where the rotary brush 2 contacts the photoreceptor 1.
As illustrated in FIGS. 8A and 8B, when the photoreceptor 1 is a drum type, the center of curvature of the surface of the photoreceptor 1 where the rotary brush 2 contacts is the center of rotation 1P of the photoreceptor 1.
FIG. 8A illustrates the rotary brush 2 and the photoreceptor 1, when the surface movement direction of the photoreceptor 1 is the same as the movement direction of the brush tip of the rotary brush 2 in the nip N. FIG. 8B illustrates the rotary brush 2 and the photoreceptor 1, when the surface movement direction of the photoreceptor 1 is opposite to the surface movement direction of the brush tip of the rotary brush 2 in the brush nip N (so-called “counter-rotation”).
In the rotary brush 2 of FIGS. 8A and 8B, the traveling direction of the dispersed toner T changes over time due to the effect of gravity such that the dispersed toner T travels toward the photoreceptor 1 further than the tangent Lt to the surface of the photoreceptor 1 at the downstream nip end E of the nip N in the rotary direction of the rotary brush.
In other words, the traveling direction of the dispersed toner T traveling in the direction toward the tangent Lt at the downstream nip end E changes to a direction separating from a brush housing 3 due to gravity. Consequently, it is difficult to prevent or collect the dispersed toner T traveling toward the tangent Lt by the brush housing 3.
Referring now to FIGS. 9A and 9B, there are provided conceptual diagrams illustrating the photoreceptor 1 and the rotary brush 2 when the center of rotation 1P of the photoreceptor 1 is at a substantially same level as the downstream nip end E of the nip N in the rotary direction of the rotary brush.
In FIG. 9A, the surface movement direction of the photoreceptor 1 is the same as the movement direction of the brush tip of the rotary brush 2 in the brush nip N. In FIG. 9B, the surface movement direction of the photoreceptor 1 is opposite to the movement direction of the brush tip of the rotary brush 2 (counter-rotation).
In the rotary brush 2 as illustrated in FIGS. 9A and 9B, even if the dispersed toner T is affected by gravity, the traveling direction of the dispersed toner T does not change. That is, the dispersed toner T does not travel toward the photoreceptor 1 further than the tangent Lt at the downstream nip end E. Particularly, the dispersed toner T traveling toward the tangent Lt at the downstream nip end E remains traveling along the tangent Lt even after being affected by gravity.
The dispersed toner T traveling to the tangent Lt at the downstream nip end E is the toner that travels to an orbit farthest away from the rotary brush 2. Other dispersed toner T travels toward the rotary brush 2 further than the tangent Lt.
Referring now to FIGS. 10A and 10B, there are provided conceptual diagrams illustrating the photoreceptor 1 and the rotary brush 2, when the downstream nip end E downstream of the brush nip N is substantially lower than the center of rotation 1P of the photoreceptor 1.
In FIG. 10A, the surface movement direction of the photoreceptor 1 is the same as the movement direction of the rotary brush 2 in the brush nip N. In FIG. 10B, the surface movement direction of the photoreceptor 1 is opposite to the movement direction of the brush tip of the rotary brush 2 (counter-rotation).
In the rotary brush 2 of FIGS. 10A and 10B, when the dispersed toner T is affected by gravity, the dispersed toner T travels toward the rotary brush 2 further than the tangent Lt to the surface of the photoreceptor 1 at the downstream nip end E. The dispersed toner T that travels to the orbit farthest away from the rotary brush 2 travels to the direction of the tangent Lt at the downstream nip end E, and when affected by gravity, the dispersed toner T travels to the rotary brush 2 further than the tangent Lt. Other toner dispersed also travels to the rotary brush 2 further than the tangent Lt.
When the photoreceptor 1 and the rotary brush 2 are disposed as illustrated in FIGS. 9A through 10B, the dispersed toner can be prevented from traveling outside the brush housing 3 by covering the rotary brush 2 side with the brush housing 3 further than the tangent Lt.
According to Japanese Patent Unexamined Application Publication No. 2005-17463, the rotary brush 2 of the cleaning unit relative to the photoreceptor 1 is positioned in a similar manner as that of FIG. 10B. According to Japanese Patent Unexamined Application Publication No. 2005-234481, the rotary brush 2 of the cleaning unit relative to the photoreceptor 1 is positioned in a similar manner as that of FIG. 10A.
However, according to the related art brush housings, a housing tip (equivalent of 3a in FIG. 10) at the downstream nip end E of the nip N in the rotation direction of the rotary brush is disposed more toward the rotary brush side than the tangent Lt. Consequently, the dispersed toner T traveling to the tangent Lt may escape through a space between the housing tip and the photoreceptor, thereby not adequately preventing the toner from traveling outside the brush housing.